The explosive growth of Uber can't be denied. In the five years since its birth in San Francisco, the ride sharing company now operates in 49 U.S cities, and 35 counties around the globe, and it has rapidly become the hottest way to get around Southern California.

The company connects those in need of a ride with drivers happy to provide the car, all through a cell phone app. There are a variety of ways to get around -- from swanky "black car" limousine service to the more modest UberX, where anyone with a car and the inclination can apply to be a driver.

That's exactly what Beverly Locke did. Working with the NBC4 I-Team, Locke filled out all the necessary documentation needed to become an Uber driver. She proved she was a licensed driver with a safe car, and agreed to submit to a background check.

Four weeks later, she received an e-mail indicating her background check had cleared.

On her first day "on the job," she received a request from Paolo, a frequent UberX user, who was looking for a ride from his Hollywood apartment. He is an Uber fan.

"I use cabs a lot," said Paolo. "And, it's almost half the fare in Uber than for a taxi driver."

His phone lit up with a picture of Locke, and a message that said Beverly will pick him up in three minutes.

What he didn't know is that Beverly was an ex-con with a violent past. Her 20-year rap sheet includes burglary, cocaine possession, and making criminal threats with the intent to cause death or bodily injury.

"I pulled a girl out of a car and almost beat her to death," said Locke, who described herself as a reformed criminal with a good job and a desire to make up for her past. "I do not do criminal things anymore."

NBC4 asked Locke to cancel the ride, so the former convict never actually carried a passenger. But the NBC4 I-Team found several examples in which drivers with a criminal past have picked up Uber passengers.

Tadeusz Szczechowicz drove the streets of Chicago for a year, despite five prior arrests and two convictions for burglary and disorderly conduct.

Syed Muzzafar had a prior conviction for reckless driving, but he cleared the Uber background check and was behind the wheel New Year's Eve when he was arrested for hitting and killing a 6-year-old girl in San Francisco.

And, Jigneshkumar Patel was arrested for battery of an UberX passenger, a charge he said is "rubbish." Still, the UberX driver had a 2012 conviction for DUI.

Uber declined to talk to NBC4 directly, but did send emails describing corporate policy on background checks. A message said Uber "leads the industry" with its "best-in-class background checks for drivers."

Uber also said it has a "zero tolerance" policy for drug and alcohol offenses, and said it carefully screens applicants and immediately disqualifies anyone convicted of a crime in the past seven years.

Tanya and Daniel Sackler didn't know anything about the past of their UberX driver. He identified himself only by his first name.

The Sacklers said he stole $2,500 in cash and personal items from them after he picked them up from LAX and dropped them off at their West Hollywood condo. The Sacklers filed a police report, saying the driver arrived at their home and quickly began unloading their baggage.

"He took them all and he put them in a pile," Daniel said.

While the Sacklers were dealing with their luggage, Tanya Sackler said their driver jumped back behind the wheel and quickly drove off with her purse, her husband's briefcase, a wallet with hundreds of dollars in it, and an iPad.

They had the driver's cell number, so they texted him right away, only to be told he was too busy to talk to them at the moment. The Sacklers said when they finally spoke to him, the driver told them he was not responsible for items left in his car.

In an email to the Sacklers, Uber told them, "We do not control the drivers, as they are not our employees." On its website, Uber said drivers are considered independent contractors.

"If I knew that this company had treated people this way, I would have never used it," Tanya said.

Beverly Locke said passengers could lose a lot more if they take a ride from an ex-con. And, picking up a passenger bound for an out-of-town trip might make for an easy target.

"I would pick somebody up, take them to the airport, and my second thought would be, go back to that house and see what's in there," she said. "A criminal mind always thinks like a criminal mind. Someone could be victimized by a person like me."

Uber spokespeople never responded to requests to talk specifically about Locke, and how she was able to pass a background check. But the NBC4 I-Team received an email from Lane Kasselman, head of communications for Uber, that said, "We screen for convictions and violations going back seven years that are reasonably related to tasks the drivers perform (DUIs, violent/sexual offenses, major moving violations, etc. A former non-violent criminal ...may be permitted... We're confident that every ride on Uber is safer than a taxi."